Field of the Invention
The present invention relates to a method and an apparatus on a turbomachine with an outer casing and an inner casing or blade carrier for thrust compensation. In particular, the area of application of the invention is in the field of turbo engines of pot-type construction, where a pressure of a fluid flowing through the turbomachine causes an axial force in the longitudinal direction of the shaft, at least on the inner casing.
It is known that, in the case of turbomachines with a high internal pressure, the casing is divided into an inner casing and an outer casing. A multi-channel casing of a steam turbine for high steam pressures and steam temperatures is described in Published, Non-Prosecuted German Patent Application DE 2 218 500 A, corresponding to U.S. Pat. No. 3,844,675. In the present configuration of the high-pressure turbine of pot-type construction, live steam enters the inner casing at a high pressure. After an expansion of about 20% of the total pressure drop of the part-turbine, the steam is passed through holes into the outer casing and thus compresses the inner casing in the region of the joints in the course of its further expansion. In subcritical steam conditions, the configuration with a blade carrier is chosen. Here, the full live-steam pressure is present in the space between the inner casing and the outer casing and thus presses the two halves of the carrier together. In the rest of the description, the term "inner casing" also includes the blade carrier in all cases. Given their superimposition, the pressures acting on various surfaces also ensure a resultant thrust on components, and this has to be absorbed by corresponding devices on the inner casing and/or outer casing and/or on the shaft. For this purpose, it is furthermore known for the interspace between the inner casing and the outer casing to be sealed off from the outlet side of the fluid flowing through the turbomachine, so that the pressure difference between the inlet and the outlet has to be accepted by the inner casing, while the outer casing has to withstand the outlet pressure on the outflow side and the pressure between the outer and inner casing relative to atmospheric pressure on the inflow side. The pressures present in the various spaces of a turbomachine ensure high axial forces, which must be transmitted via corresponding devices such as, for example, bayonet rings, threaded rings, Uhde-Brettschneider fasteners or screwed fastenings, to the outer casing or other suitable devices. In addition to possible large deformations, the forces also give rise to high surface pressures on corresponding supports.
The Published, Non-Prosecuted German Patent Application DE 2 218 500 A, for example, discloses a multi-shell casing of a steam turbine for high steam pressures and steam temperatures. An inner shell is clamped against the outer casing by a supporting ring and thus fixed axially. U.S. Pat. No. 3,754,833, in turn, and its priority document, German Patent DE 20 54 465 B2, describes a device for mounting and centering of shaft seal housings on the outer casing shells of turbomachines in a manner which allows thermal movement in a radial and concentric fashion. The turbine illustrated there has a pot-type casing with a joint normal to the axis. An inner casing carrying the fixed blades is inserted into the pot-type casing at a bearing and centering location. This centering location is formed by an Uhde-Brettschneider fastener. In the region of the shaft lead-throughs through the pot-type casing there are shaft seal housings on which sealing covers are mounted. Bypass passages in the inner casing serve for axial thrust compensation.
The constructional outlay in the case of turbomachines for absorbing the axial forces is, as explained above, very high overall. Since the efficiency of a turbomachine is greatly influenced by flow losses, the thrust forces must furthermore be absorbed in such a way that, given corresponding thermal expansions of the shaft and of the inner and outer casing, the radial gaps at the blade ends are as small as possible.